The Hannya Shingyo is called The Heart Sutra because it represents the heart of great wisdom. It was written between the 1st and 6th centuries of our era. Common to all lineages of buddhism, it is certainly the most well-known sutra. The bodhisattva Avalokitesvara gives a teaching to Sariputra on the emptiness of all beings and all things, because none of them possesses a fixed or substantial character. Everything is impermanent and exists in interdependence and not solely by itself.
The Hannya Shingyo is chanted during the ceremony that follows zazen, in its Kanbun form (ancient phonetic-sanskrit-ancient chinese):
Text in kanbun (classical chinese)

Text in kanbun (phonetic)
Maka Hannya Haramita Shingyo
Kan ji zai bo satsu. Gyo jin han-nya ha ra mi ta ji. Sho ken go on kai ku. Do is-sai ku yaku. Sha ri shi. Shiki fu i ku. Ku fu i shiki. Shiki soku ze ku. Ku soku ze shiki. Ju so gyo shiki. Yaku bu nyo ze. Shari shi. Ze sho ho ku so. Fu sho fu metsu. Fu ku fu jo. Fu zo fu gen. Ze ko ku chu. Mu shiki mu ju so gyo shiki. Mu gen ni bi ze-shin ni. Mu shiki sho ko mi soku ho. Mu gen kai nai shi mu i shiki kai. Mu mu myo yaku mu mu myo jin. Nai shi mu ro shi. Yaku mu ro shi jin. Mu ku shu metsu do. Mu chi yaku mu toku. I mu sho toku ko. Bodai sat-ta. E han nya ha ra mi ta ko. Shin mu kei ge mu ke ge ko. Mu u ku fu. On ri is-sai ten do mu so.Ku gyo ne han. San ze sho butsu. E han-nya ha ra mi ta ko. Toku a noku ta ra san myaku san bo dai. Ko chi han-nya ha ra mi ta. Ze dai jin shu. Ze dai myo shu. Ze mu jo shu. Ze mu to do shu. No jo is-sai ku. Shin jitsu fu ko. Ko setsu han-nya hara mi ta shu. Soku setsu shu watsu.
Gya tei gya tei hara gya tei.
Hara so gya tei bo ji so wa ka.
Han-nya shin gyo.
Translation
Essence of the Sutra of Great Wisdom that allows one to go beyond
The Bodhisattva of True Freedom and compassion, through the profound practice of Great Wisdom, understands that the body and the five skandas (sensation, perception, thought, activity, consciousness) are only emptiness, Ku, and through this understanding, he helps all those who suffer.
O, Sariputra, phenomena are not different from Ku, Ku is not different from phenomena. Phenomena become Ku, Ku becomes phenomenon (form is emptiness, emptiness is form), the five skandas are phenomena as well.
O, Sariputra, all existence has the character of Ku, there is neither birth, nor beginning, nor purity, nor defilement, nor growth, nor decrease. That is why, in Ku, there is neither form, nor skandas, nor eye, nor ears, nor nose, nor tongue, nor body, nor consciousness.
There are neither colors, nor sounds, nor smell, nor taste, nor touch, nor object of thought. There is neither knowledge, nor ignorance, nor illusion of decline and death. There is neither origin of suffering, nor cessation of suffering. There is no knowledge, nor profit, nor non-profit.
For the Bodhisattva, thanks to this Wisdom that leads beyond, there is neither fear, nor dread.
All illusion, all attachment are removed and he can grasp the ultimate end of life, Nirvana.
All the Buddhas of the past, present and future, by this incomparable and unsurpassable incantation (mantra) which allows one to find authentic reality, Ku, can attain the understanding of this Supreme Wisdom which delivers from all suffering.
Here is this incantation:
Go, go, go together beyond the beyond to the shore of Satori.